Causes and solutions for cracks and warpage of stamping and bending parts

First, cracks appear in stamping and bending parts. Bending cracks mostly occur when the bending radius and bending angle requirements are too strict. For products with a small bending width, the cracks are at both ends of the width; when the bending width is large, the cracks occur along the bending line and near the middle of the bending width. In addition, the bending line often produces cracks in the right-angled part. The method of eliminating cracks in stamping and bending parts: (1) Measures to be taken when cracks occur along the bending line. ①When the radius of curvature is constant, the thicker the sheet or the longer the bending width, the easier it is to produce cracks. Using SPCC type steel plate, such as R/t<0.5, cracks will occur. Therefore, R/t is designed to be 0.5 or more to avoid cracks. ② Make the bending line at right angles to the fiber direction. However, the bending limit of the rolled material is different in the fiber direction and the vertical direction. When the bending process is close to the limit, the relationship between the bending line and the fiber direction when the sheet is blanked must be considered. ③The burr side is placed on the inner side of the curve. ④Remove burrs. ⑤ Anneal only the burr part of the curved line. ⑥ Compress the cut surface of the burr to a 45 degree angle, and then bend it. ⑦When the bending limit of the thick plate is exceeded and it is bent to a small R, the additional back pressure method is used. In this method, in the free bending mold, the lower mold uses a strong top material plate, which can increase the compressive stress on the deformed part of the plate during the bending process, so that the minimum bending radius can be significantly reduced and cracks can be prevented. After completing the V-shaped bending, a platform is formed on the outside of the bending radius of the product, which is caused by the back pressure of the top material. (2) Measures to be taken when cracks occur in the part at right angles to the bending line. ①Move the curve back from the end face of the blank (2t+R), or align the bending line with the end face of the blank, and then make an empty groove of (1.5-2.0t+R). ②When performing hollow bending processing, first consider punching out a groove 2 to 3 times larger than the plate thickness, and then bending it, or opening a circular process hole in the previous process, and then performing punching (notch) bending processing. Second, the bending line of the stamped and bent part appears on the outside due to the tensile stress, resulting in compression deformation, and there are opposite stress and strain on the inside, so the product will be saddle-shaped. When H/t is less than 6-7, the warpage rate H/t is at most 2/1000, and when it is greater than 6-7, the warpage rate is less than 1/1000. It has nothing to do with material and rolling direction. The method of eliminating the warpage of the stamping and bending parts: (1) When the warpage of the thin plate is very small, the cavity should be close to the central part of the bending line. (2) When the processing conditions are strict, first measure the amount of warpage, and secondly, make the punch reverse bending only according to the amount of warpage. This reverse bending method is best to clamp between the punch and the mold base with a bushing and fix it at both ends. Previous post: What principles should be followed when choosing cutting fluid for machining?